AMC 8 1988 Problem 23
AMC8 1988 年第 23 题
比与比例★★★☆☆
Maria buys computer disks at a price of 4 for $5 and sells them at a price of 3 for $5 . How many computer disks must she sell in order to make a profit of $100 ?
Maria 以 $5 买 4 张的价格购入计算机磁盘，以 $5 卖 3 张的价格出售。为获得 $100 利润，她必须卖出多少张磁盘？
- A.100
- B.120
- C.200
- D.240
- E.1200
正确答案 · Correct Answer
D
解析 · Solution
Solution 1
Maria buys at dollars per disk and sells at dollars per disk, so her profit is - = dollars per disk. Thus to make a profit of $100 she must sell disks. This is valid since 240 is divisible by both 3 and 4, and therefore Maria will not have any disks left over.
If Maria buys 12 disks, she buys 3 sets of 4 so she pays $15. If Maria sells 12 disks, she sells 4 sets of 3 so she gets $20. Therefore, for every 12 disks Maria sells, she profits $5.
To profit $100, she must sell batches of 12 disks, for a total of 240 disks.
继续练习